Thymeleaf List工具方法

1. Overview

Thymeleaf is a Java template engine for processing and creating HTML.

In this quick tutorial, we’ll look into Thymeleaf’s lists utility object to perform common list-based operations.

2. Computing Size

First, the size method returns the length of a list. We can include it, say, via the th:text attribute:

size: <span th:text="${#lists.size(myList)}"/>

myList is our own object. We’d have passed it via the controller:

@GetMapping("/size")
public String usingSize(Model model) {
    model.addAttribute("myList", getColors());
    return "lists/size";
}

3. Checking If the List Is Empty

The isEmpty method returns true if the given list has no elements:

<span th:text="${#lists.isEmpty(myList)}"/>

Generally, this utility method is used with conditionals – th:if and th:unless:

<span th:unless="${#lists.isEmpty(myList)}">List is not empty</span>

4. Checking Membership

The contains method checks whether an element is a member of the given list:

myList contains red: <span th:text="${#lists.contains(myList, 'red')}"/>

Similarly, we can check the membership of multiple elements using the containsAll method:

myList contains red and green: <span th:text='${#lists.containsAll(myList, {"red", "green"})}'/>

5. Sorting

The sort method enables us to sort a list:

sort: <span th:text="${#lists.sort(myList)}"/>

sort with Comparator: <span th:text="${#lists.sort(myList, reverse)}"/>

Here we have two overloaded sort methods*.* Firstly, we’re sorting our list in the natural order – ${#lists.sort(myList)}. Secondly, we’re passing an additional parameter of type Comparator. In our example, we’re getting this comparator from the model.

6. Converting to List

Lastly, *we can convert Iterables and arrays to Lists using the toList method.*

<span th:with="convertedList=${#lists.toList(myArray)}">
    converted list size: <span th:text="${#lists.size(convertedList)}"/>
</span>

Here we’re creating a new List, convertedList, and then printing its size with #lists.size.

7. Summary

In this tutorial, we’ve investigated the Thymeleaf built-in lists utility object and how to use it effectively.

As always, the source code for all examples is available over on GitHub.